The present invention relates to an LCD (Liquid Crystal Display) video projector for projecting an image in LCD panel enlarged on a screen, more specifically, an LCD video projector that can move the location of a projected picture by shifting the standing of projection lens up and down.
There have been an LCD video projector for magnifying and projecting an image in LCD panel on a screen using a metal halide lamp, etc. as a light source. In such projector, the light from a light source is concentrated through a mirror or such other devices on an LCD panel, and an image existing in the LCD panel is projected through a projection lens on a screen.
Normally in an LCD video projector, the center of LCD panel is located on the optical axis of projection lens, hence a picture is projected on a screen with its center and the optical axis of projection lens met. The video projector is usually placed on a flat horizontal plane such as a desk top, however, because a preferred positioning of projected picture is usually higher than the desk top, the video projector is often uplifted in its front part by, for example, extending front feet of the video projector. A drawback with the above described arrangement is that a projected picture is distorted to a trapezium shape. A means to solve the above drawback is to design a projection apparatus so as to be able to shift the optical axis of projection lens relative to the center axis of LCD panel, and project an image with the respective axes dislocated from each other.
Prior art mechanism's for shifting the optical axis of lens are illustrated in FIGS. 8-10. FIG. 8 is a perspective view of such a mechanism disclosed in the Japanese Patent Laid-open No.5-27324. In which mechanism, a condenser lens 52 and a projection lens 53 mounted on an arm 54 may be moved up and down by turning a screw shaft 55. The optical axis is thus shifted from the center axis of an LCD panel.
FIG. 9 is a side view of such a mechanism disclosed in the Japanese Utility Model Laid-open No.5-21246. In which mechanism, a projection lens 61 is mounted on a pantograph pedestal supported with an operation link 62 and a link 63, and the projection lens 61 is moved up and down while being kept in parallel by turning a gear 64 engaged with the operation link 62.
FIG. 10 is a side view of such a mechanism disclosed in the Japanese Patent Laid-open No.8-160488. In which mechanism, a lens barrel 71 is moved up and down by revolving a pinion 72 of a motor attached to the lens barrel 71, the pinion 72 being engaged with straight line gear teeth 74 on a rack 73.
Problems with these prior art LCD video projector having above described types of lens moving mechanism include a complexity and bulkiness of the lens moving mechanism, a large number of assembly parts and components needed for the lens moving mechanism as well as a high manufacturing cost coming therefrom, also a not-quite-satisfactory operational convenience. In the case of FIG. 8, for example, two shafts have to be revolved synchronized by a gear transmission, which means that a precise position setting is not quite easy, and it requires a rather complicated mechanism occupying a bulky space. In the case of FIG. 9, the link portion readily causes a play, which results in a difficulty of focusing. The span of up and down motion is limited because of the pantograph structure. In the case of FIG. 10, in which a motor and a gear wheel are integrated, space for housing the motor, etc. and manufacturing cost are the drawbacks.
Along with the increasing use of LCD video projector, voices have become louder for a new LCD video projector that is compact and easy, as well as comfortable, to use.